musl/arch/x86_64/ksigaction.h

struct k_sigaction {
	void (*handler)(int);
	unsigned long flags;
	void (*restorer)(void);
	unsigned mask[2];
};

void __restore_rt();
#define __restore __restore_rt
work around gdb issues recognizing sigreturn trampoline on x86_64 gdb can only backtrace/unwind across signal handlers if it recognizes the sa_restorer trampoline. for x86_64, gdb first attempts to determine the symbol name for the function in which the program counter resides and match it against "__restore_rt". if no name can be found (e.g. in the case of a stripped binary), the exact instruction sequence is matched instead. when matching the function name, however, gdb's unwind code wrongly considers the interval [sym,sym+size] rather than [sym,sym+size). thus, if __restore_rt begins immediately after another function, gdb wrongly identifies pc as lying within the previous adjacent function. this patch adds a nop before __restore_rt to preclude that possibility. it also removes the symbol name __restore and replaces it with a macro since the stability of whether gdb identifies the function as __restore_rt or __restore is not clear. for the no-symbols case, the instruction sequence is changed to use %rax rather than %eax to match what gdb expects. based on patch by Szabolcs Nagy, with extended description and corresponding x32 changes added. 2016-11-13 00:43:37 +00:00			`struct k_sigaction {`
			`void (*handler)(int);`
			`unsigned long flags;`
			`void (*restorer)(void);`
			`unsigned mask[2];`
			`};`

			`void __restore_rt();`
			`#define __restore __restore_rt`